grandson of the preceding, was the son and successor of Ariobarzanes III. He was a minor at the death of his father but the period of his accession cannot be determined. Clinton places it as low as 242 or 240 B. C., while Droysen (Hellenism. vol. ii. p. 355) carries it back nearly to 258. It seems probable that it must be placed considerably before 240, as Memnon tells us that he was a child at his father's death, and he had a daughter of marriageable age in 222. Shortly after his accession his kingdom was invaded by the Gauls, who were, however, repulsed. (Memnon, 100.24, ed. Orell.) After he had attained to manhood he married a sister of Seleucus Callinicus, with whom he is said to have received the province of Phrygia as a dowry. (Euseb. Arm. p. 164; Just. 38.5.) But notwithstanding this alliance, we find him, during the war between Seleucus and Antiochus Hierax, taking part against the former, whom he defeated in a great battle, in which Seleucus lost 20,000 of his troops, and narrowly escaped with his own life. (Euseb. Arm. p. 165.) In B. C. 222, Mithridates gave his daughter Laodice in marriage to Antiochus III.: another of his daughters, also named Laodice, was married about the same time to Achaens, the cousin of Antiochus. (Plb. 5.43, 74, 8.22.) In B. C. 220 Mithridates made war upon the wealthy and powerful city of Sinope, but it appears that he was unable to reduce it, and it did not fall into the power of the kings of Pontus until long afterwards. (Id. 4.56.) At an earlier period we find him vying with the other monarchs of Asia in sending magnificent presents to the Rhodians, after the subversion of their city by an earthquake. (Id. 5.90.) The date of his death is unknown, but Clinton assigns it conjecturally to about B. C. 190. He was succeeded by his son Pharnaces. [PHARNACES I.]